To not go on MIL's birthday day out?

It's DP's mums birthday today. We're in the process of moving in together, we got our keys today so he's been moving everything in. I couldn't get the day off work so he's been doing it with his parents and my family. I won't finish work till 6 and won't get home till 7, I've worked a 46 hour week and I'm 19 weeks pregnant. I'm exhausted. His mum wants to go to the seaside tomorrow for her birthday. This will involve a 4 hour round trip and me being sat in the back squashed between DP and his sister. He won't take us in his own car as he doesn't want to pay the petrol money. I'm so uncomfortable sat down for a long period of time and I just want to spend my only day off this week sorting our new apartment out and unpacking everything. I don't want to spend it in a car for 4 hours and then having to listen to his mum and sister talk incessantly about the baby all day. AIBU to stay at home? He says I'm being rude and ungrateful.

I think I would phone mil and explain that the position of the baby would make it too painful / uncomfortable for you to squash in the back of a car with 2 adults - perhaps she could persuade her son to drive ?

I think that you should go although it sounds very much like you have decided not to. Alternatively arrange a nice meal out with in laws and partner as a thankyou for their help with the move? You're setting a tone for the future on this one. MIL being interested in the baby is lovely. takes time and effort to build relations with ILs.

I think DP is at fault here for being so petty about the petrol money. If you tire early out in the sun you will need the means to get home by yourself. You really won't want to be waiting on everyone else.

He must put you and the baby first, and I am sure his mother would understand if you had to leave early. Just knowing you have that option will make you feel better and you might last the whole day.

You can sort the flat out next weekend, but it would be nice to celebrate with MIL tomorrow especially as she has been so helpful today.

I agree with with every one else only go if you go in his car! And if I read it right your parents helped with the move so PIL didn't have to. Am really not liking the penny pinching re petrol and guilt tripping you just as you move in together, and whilst your pregnant! Not a good combination